Thanks for this helpful guide! My Harmony Ultimate One purchased used without cradle and exhibits these symptoms. I suspect a bad battery, but wanted to post here before spending $20 for a battery.
1. On USB power (not PC), very short flash of all white then “Harmony®” briefly, then myharmony.com image is displayed. Shutting off then causes the white flash, Harmony® and myharmony.com sequence.
2. Connect USB to Windows laptop, off button causes the white flash, Harmony® and myharmony.com sequence again. Launch and login to MyHarmony app. Click on Harmony Ultimate One icon – synching popup shows progress, then goes away. Click on Sync button prompts a “Sync in progress” screen. “Retrieving your device & activity settings” and progress indicator stalls at 33% complete…wait for 30 minutes, “low battery” screen appeared briefly, then the white screen flashes, Harmony® screen is displayed.
3. Removed USB cable from PC to charging power supply and left overnight to charge. No change on remote display.